URI: 

       Title: Crop a video using ffmpeg
       Author: Solène
       Date: 20 December 2019
       Tags: ffmpeg
       Description: 
       
       If you ever need to crop a video, which mean that you want to reduce
       the area
       of the video to a square of it to trim areas you don't want.
       
       This is possible with ffmpeg using the video filter **crop**.
       To make the example more readable, I replaced values with variables
       names:
       
       - WIDTH = width of output video
       - HEIGHT = height of output video
       - START_LEFT = relative position of the area compared to the left, left
       being 0
       - START_TOP = relative position of the area compared to the top, top
       being 0
       
       So the actual commands look like
       
           ffmpeg -i input_video.mp4 -filter:v
       "crop=$WIDTH:$HEIGHT:$START_LEFT:$START_TOP" output_video.mp4
       
       
       If you want to crop the video to get a 320x240 video from the top-left
       position 500,100 the command would be
       
           ffmpeg -i input_video.mp4 -filter:v "crop=320:240:500:100"
       output_video.mp4